This application focuses on the long term goal of stimulating -cell regeneration as a cure for diabetes. The mechanism controlling the cell cycle progression of -cells keeps them at an extremely low proliferating state that decreases further with age. Using a model that we have previously shown to exhibit enhanced -cell regeneration, we plan to test the hypothesis that p16 and cyclin D are responsible for the observed slow regeneration phenotype. PTEN (phosphatase and tensin homologue deleted on chromosome 10) is a negative regulator of a particular -cell mitogenic signal, PI3K/AKT. We have shown that loss of PTEN in - cells leads to increased islet mass and mitotic activity. To evaluate the molecular mechanisms responsible for this phenotype, we explored various cell cycle regulators and discovered that cyclin D and p16 are significantly altered in the islets. We followed this initial observation and confirmed that PTEN can directly regulate p16 and cyclin D using a glioma cell line. Because of the correlation of p16 upregulation with loss of regeneration in aged -cells, we hypothesized that PTEN loss may be capable of inducing regeneration of - cells in even older mice. Our preliminary data showed that this is possible in adult mice without the contribution of developmental deletion of Pten. To demonstrate this result, we employed a model that can induce the deletion of Pten in adult mice. Together, these data led to the current hypothesis that PTEN regulates regeneration of b-cells through p16 and cyclin D. To test this hypothesis, we have planned three specific aims: First, we will investigate whether the mitotic activity in -cells induced by PTEN loss depends on p16 and cyclin D. Second, we will determine if loss of PTEN is capable of inducing regeneration of -cells in mice beyond the age (1 year) at which physiological stimuli can no longer enhance -cell regeneration. Third, we will determine whether PTEN regulates p16 through PI3K/AKT signaling. The results from this analysis will substantially improve the understanding of how -cells regenerate and shed light on what molecules need to be manipulated to promote their regeneration.